1) Field of the Invention
This invention generally relates to a plasma reactor and a method of processing a substrate with a plasma generated in the reactor. More particularly, the invention relates to utilizing a pulsed plasma processing apparatus and method configured to generate a plasma having a lower temperature than conventional plasma processing reactors.
2) Discussion of Related Art
The manufacture of integrated circuits involves the manufacture of field effect transistors in and on silicon or other semiconductor substrates. The manufacture of a field effect transistor includes the formation of a gate dielectric layer. The dielectric layer is typically grown by exposing silicon of the substrate to oxygen, thereby forming silicon dioxide gate dielectric layers.
As logic devices have become smaller, it has become advantageous to include nitrogen into the silicon dioxide gate dielectric layers. Nitrogen is often incorporated by creating a plasma of nitrogen ions within a chamber and implanting the nitrogen ions into the gate dielectric layer. The plasma is typically created utilizing a radio frequency (RF) source, with either an electrode plate (capacitative coupling) or a coil (inductive coupling). The RF source creates an RF field within a gas in the chamber, and this coupling creates the plasma.
Independent of the type of RF source (plate or coil), there can be significant capacitative coupling from the source to the plasma, which creates a relatively large plasma potential, on the order of tens of volts. Such a large plasma potential may cause excessive bombardment of the silicon dioxide layer with nitrogen ions, which can cause damage to the silicon dioxide layer and even incorporation of nitrogen into the underlying silicon. Damage to the silicon dioxide layer or incorporation of nitrogen into the underlying silicon diminishes the advantages of nitrogen incorporation.
According to one aspect of the invention, a method is provided of processing a substrate, including locating the substrate in a processing chamber, creating a nitrogen plasma in the chamber, the plasma having an ion density of at least 1010 cmxe2x88x923, and a potential of less than 20 V, and exposing a layer on the substrate to the plasma to incorporate nitrogen from the plasma into the layer.
According to another aspect of the invention, a method of processing a substrate is provided, wherein the substrate is located in a plasma processing chamber, a nitrogen-containing gas flows into the chamber, an RF current is provided through a coil to generate an RF field in the chamber, the RF field creating a nitrogen-containing RF plasma out of the gas, the RF current being pulsed, and incorporating nitrogen ions and excited neutrals from the plasma into a gate dielectric layer formed on the substrate.
According to a further aspect of the invention, a plasma reactor is provided, including a chamber having an opening to transfer a substrate into an internal volume of the chamber, a substrate holder in the chamber for holding the substrate, an RF coil externally and adjacent to a wall of the chamber, and a grounded electrode plate between the wall and the RF coil.
Embodiments of the invention further provide a method of forming a nitride gate dielectric layer. The method includes generating a nitrogen-containing plasma in a processing chamber via introduction of a nitrogen-containing processing gas into the processing chamber and the application of an ionizing energy to the processing gas, and pulsing the ionizing energy to maintain a mean temperature of electrons in the nitrogen-containing plasma of less than about 0.7 eV.
Embodiments of the invention further provide a method of controlling a mean energy of constituents of a nitrogen-containing plasma used to nitridate a gate dielectric layer, comprising pulsing an ionizing source used to maintain the nitrogen-containing plasma for a first duration sufficient to energize the nitrogen-containing plasma and turning off the ionizing source and allowing the constituents of the nitrogen-containing plasma to dissipate for a second duration, the second duration being longer than the first duration, and the second duration being calculated to generate a mean energy of the constituents of a nitrogen-containing plasma of less than about 0.7 eV.